1. Field of the Invention
This invention relates to humidifiers in general and to residential humidifiers in particular. As is well known, such humidifiers are used to increase the humidity in the room in which they are located as well as adjacent rooms. It is well known that increasing the humidity level in a dry room makes it more comfortable for the room's occupants. Present day ultrasonic room humidifiers, which are in widespread use today, have a significant disadvantage in that their use results in a coating of white dust on surfaces in the room.
2. Description of the Prior Art
Early humidifiers were primarily used by ill persons suffering with chest congestion. Humidifiers of this type were called vaporizers and created water vapor through the application of heat. Warm, moist air or vapor channeled directly to the patient.
Residential humidifiers are used to increase the humidity level in one or more rooms having very dry air. This is frequently found in homes with forced hot air heating systems. The room humidity generally decreases as the outside air temperature decreases. As the humidity level drops the discomfort level increases. Of course, very dry air is also found in homes in hot desert geographical areas. One solution to this problem has been the introduction of so-called cold air room humidifiers. These humidifiers are more desirable for general room use than vaporizers with heating elements, as the high localized humidity levels which they create for patients is not required for increasing the humidity levels in a room under normal circumstances. These humidifiers also have larger water reservoirs and use less water per hour, thus increasing the time between reservoir refills. Some cold air humidifiers accomplish their purpose by rotating a porous wheel or drum made of a sponge-like material through water. A fan blows air through the porous material thus causing the water to evaporate, increasing the humidity in the room.
One of the problems with the cold air humidifiers of this type is their relatively large size. Another problem has been the buildup of "scale" on the porous drum. This buildup of scale can be minimized through the use of additives; however, their use is both costly and inconvenient. Ultimately, the porous drums must be replaced. The large size problem of residential room humidifiers of this type was solved with the advent of vaporization humidifiers.
In vaporization humidifiers the small water droplets caused by the atomization of the water, evaporate subsequent to their ejection into a room. However, dissolved substances, e.g., minerals and the like, contained in the water precipitate out of solution when the water evaporates. Since the atomized water droplets are very small, the amount of solid substances which remain after evaporation is quite small. These particles are the white dust found on surfaces in rooms where vaporization humidifiers are used.
It is these minerals which also form the scale in the rotating porous member of the rotating drum humidifiers. In the hot air vaporizer, the concentration of minerals increases in the water which remains and, if the water is completely used, may be found as deposits on the bottom of the water container. Similar deposits are found in the bottom of a pan when water is permitted to boil off or evaporate.
Distilled water may be used to eliminate the dust problem associated with vaporization humidifiers. Since distilled water has no minerals in it, no dust can form as a result of its use. However, its cost and the inconvenience of using it on a regular basis make its use undesirable.
Ultrasonic humidifiers are the primary type of atomization residential humidifiers currently in use and are much smaller than the drum type humidifier. Ultrasonic humidifiers operate by permitting water from a removable reservoir to pass to a chamber containing an ultrasonic transducer. A vibrating surface of the ultrasonic transducer causes the water to be atomized. A fan ejects the air containing the atomized water into the room. However, ultrasonic humidifiers still have a problem. In ultrasonic humidifiers the dissolved minerals cause deposits or scale to build up on the ultrasonic transducer. This decreases its effectiveness. In some cases where the dissolved mineral concentrations are high, as in areas having very hard water, the transducer can become ineffective in as little as one week of high usage.
A solution to the "white dust" problem is proposed in U.S. Pat. No. 5,354,515 issued Oct. 11, 1994, to Ushimaru. Ushimaru appears to attribute the white dust to sodium chloride. The solution taught by Ushimaru uses permeable membranes to separate the water reservoir of humidifiers into 5 chambers. The end chambers contain electrodes.
When a voltage is applied to electrodes of Ushimaru, the dissolved sodium chloride ions are driven into the two end chambers containing the electrodes and into the middle chamber using membranes specifically chosen for the sodium and chloride ions. The water in the remaining two chambers is purified, i.e., the salt is removed therefrom or at least substantially reduced, and the water is channeled to the ultrasonic transducer for use in humidifying the room. The water, having the concentrated levels of salt, is channeled to a separate storage container from which it is ultimately removed and disposed of. In summary, Ushimaru removes the dissolved minerals from the water before it reaches the transducer in such a manner that scale is not deposited on the electrodes. The invention taught by Ushimaru patent attempts to keep mineral ions suspended in water and away from electrodes, requiring the use of membranes, and a specific membrane based on the presence of each different mineral ion.
It is an obvious disadvantage of Ushimaru that only a portion of the water contained in the reservoir is used for humidifying purposes while the remaining water is thrown away. Furthermore, the membrane chosen for a particular metal ion (e.g. Na.sup.+) may not be useful for other metal ions such as CA.sup.++, Mg.sup.++, etc. Hence, it may not be feasible to remove all types of metal ions with one or two membranes. Ushimaru asserts that an advantage of the invention described therein is that since no substances are deposited on the electrodes they do not require replacement for that reason.